Immersion photolithography system and method using microchannel nozzles

ABSTRACT

A liquid immersion photolithography system includes an exposure system that exposes a substrate with electromagnetic radiation and includes a projection optical system that focuses the electromagnetic radiation on the substrate. A liquid supply system provides liquid flow between the projection optical system and the substrate. The liquid supply system including a plurality of inlets to supply the liquid to the space, the inlets located between the table and a surface of the optical element, the surface arranged to be in contact with the liquid.

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/186,211, filed on Jul. 19, 2011, which is a continuation ofU.S. patent application Ser. No. 12/060,514, filed on Apr. 1, 2008, nowU.S. Pat. No. 8,004,649,which is a continuation of U.S. patentapplication Ser. No. 11/053,328, filed on Feb. 9, 2005, now U.S. Pat.No. 7,411,650, which is a continuation of U.S. patent application Ser.No. 10/464,542, filed on Jun. 19, 2003, now U.S. Pat. No. 6,867,844,each of the foregoing applications incorporated herein its entirety byreference.

FIELD

The present invention relates to liquid immersion photolithography, andmore particularly, to a method and a system for controlling velocityprofile of liquid flow in an immersion photolithographic system.

BACKGROUND

The practical limits of optical lithography assume that the mediumthrough which imaging is occurring is air. This practical limit isdefined by the effective wavelength equation

${\Lambda_{eff} = \frac{\lambda}{2 \cdot n \cdot {NA}}},$where λ is the wavelength of incident light, NA is the numericalaperture of the projection optical system, and n is the index ofrefraction of the medium. Now, by introducing a liquid (instead of theair) between a last lens element of the projection optical system and awafer being imaged, the refractive index changes (increases), therebyenabling enhanced resolution by lowering the effective wavelength of thelight source. Lowering a light source's wavelength automatically enablesfiner resolution of smaller details. In this way, immersion lithographybecomes attractive by, for instance, effectively lowering a 157 nm lightsource to a 115 nm wavelength, thereby gaining resolution while enablingthe printing of critical layers with the same photolithographic toolsthat the industry is accustomed to using today.

Similarly, immersion lithography can push 193 nm lithography down to 145nm. In theory, older technology such as the 193 nm tools can now stillbe used. Also, in theory, many difficulties of 157 nm lithography—largeamounts of CaF₂, hard pellicles, a nitrogen purge, etc. —can be avoided.

However, despite the promise of immersion photolithography, a number ofproblems remain, which have so far precluded commercialization ofimmersion photolithographic systems. These problems include opticaldistortions. For example, during immersion lithography scanning,sufficient g-loads are created that can interfere with systemperformance. These accelerative loads can cause a vibrational, fluidicshearing interaction with the lens resulting in optical degradation. Theup and down scanning motions within the lens-fluid environment ofImmersion Lithography can generate varying fluidic shear forces on theoptics. This can cause lens vibrational instability, which may lead tooptical “fading”. Other velocity profile non-uniformities can also causeoptical distortions.

SUMMARY

The present invention is directed to an immersion photolithographysystem with a near-uniform velocity profile of the liquid in theexposure area that substantially obviates one or more of the problemsand disadvantages of the related art.

There is provided a liquid immersion photolithography system includingan exposure system that exposes a substrate with electromagneticradiation, and includes a projection optical system that focuses theelectromagnetic radiation on the substrate. A liquid supply systemprovides liquid flow between the projection optical system and thesubstrate. A plurality of micronozzles are optionally arranged aroundthe periphery of one side of the projection optical system so as toprovide a substantially uniform velocity distribution of the liquid flowin an area where the substrate is being exposed.

In another aspect there is provided a liquid immersion photolithographysystem including an exposure system that exposes an exposure area on asubstrate with electromagnetic radiation and includes a projectionoptical system. A liquid flow is generated between the projectionoptical system and the exposure area. A microshower is at one side ofthe projection optical system, and provides the liquid flow in theexposure area having a desired velocity profile.

Additional features and advantages of the invention will be set forth inthe description that follows. Yet further features and advantages willbe apparent to a person skilled in the art based on the description setforth herein or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGS

The accompanying drawings, which are included to provide a furtherunderstanding of the exemplary embodiments of the invention and areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and together with the description serve toexplain the principles of the invention. In the drawings:

FIG. 1 shows a side view of a basic liquid immersion photolithographysetup.

FIG. 2 shows a plan view of the setup of FIG. 1.

FIG. 3 shows the basic liquid immersion photolithography setup withliquid flow direction reversed, compared to FIG. 1.

FIG. 4 shows additional detail of the liquid immersion photolithographysystem.

FIG. 5 shows a partial isometric view of the structure of FIG. 4.

FIG. 6 shows an exemplary liquid velocity profile.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

One major problem in immersion photolithography is the non-uniformity ofthe liquid flow, particularly its gradient in the vertical direction.The non-uniformity is due primarily to the fact that near a movingsurface, the liquid is in contact with that surface (e.g., a surface ofa wafer). For example, during scanning, the wafer moves relative to theexposure system, creating a “dragging effect” near its surface. Thus,the laws of fluid dynamics dictate that the fluid velocity relative tothe wafer surface is zero in those areas (or at least close to zero),while fluid velocity is maximum further away from the wafer surface.Similarly, the fluid velocity relative to the bottom surface of the lensis zero. These fluid velocity variations are known as “boundary layer”velocity profiles. The combination of these effects produces a shearingforce in the liquid that creates a twofold optical distortionproblem: 1) the generation of inertial vibrational forces upon theaperture hardware (resulting in optical distortion), and 2) theformation of velocity striations within the fluid, which causeadditional optical distortions.

Additionally, injection of liquid into the exposure area also provides aliquid flow with potential additional non-uniformities in the velocitydistribution. For example, a number of striations can exist within thefluid, further degrading exposure quality. Similarly, air bubbles,opto-fluidic vibrations, or turbulence in the liquid flow also candegrade the overall performance of the photolithographic system becauseof the introduction of optical distortions into the exposure process.Thus, dealing with velocity profile non-uniformities is important fromthe perspective of the quality of imaging in a photolithographic system.In the ideal case, the velocity profile of the liquid is substantiallyuniform everywhere.

FIG. 1 illustrates a liquid immersion photolithographic system of thepresent invention in a block diagram form. As shown in FIG. 1, aprojection optical system 100 of a photolithographic tool includes alens 102 (which is typically comprised of multiple lens elements). Inthis figure, the lens 102 has a flat bottom surface 108, although thatneed not be the case. Lens height 409 (see FIG. 4) may be adjustable tomaintain a specific distance to the wafer 101.

The projection optical system 100 also includes a housing 103 (only thelower portion is shown). The housing 103 includes an annular liquidchannel 105A, and optionally a plurality of other such channels 105B,etc. Liquid flows through the channels 105 (flowing in through thechannel 105A in this figure, and flowing out through the channel 105B).The arrows 107A, 107B designate the direction of liquid flow over awafer 101, as the wafer 101 is being scanned across a field of view ofthe projection optical system 100.

FIG. 2 illustrates a bottom-up view of the structure shown in FIG. 1. Asshown in FIG. 2, a clear aperture area 216 defines an exposure area ofthe projection optical system 100 and the lens 102. The various arrows107A-107D, 211A-211D illustrate possible liquid flow directions at anygiven time. As may be further seen in FIG. 2, the housing 103 alsoincludes a number of pressurized chambers 215A-215D. Each pressurizedchamber 215 may also be referred to as a “plenum.” The plenum 215therefore acts as a pressure source, as discussed below. It will also beappreciated that the liquid flow can be turned off completely when noexposure is taking place, or when the wafer 101 is being swapped.

Further, as shown in FIG. 2, the lower portion of the housing 103 may bedivided into a number of sections. In this figure, there are four suchsections (quadrants), separated by gaps 217A-217D. It will beappreciated that the number of such sections may be more or fewer thanfour, although, in most applications, it is expected that four quadrantsis an optimal number. For example, for motion only along one axis,dividing the housing 103 into two sections may be sufficient. For X-Ymotion, four sections (quadrants) are preferred. For even greatercontrol, eight sections may be needed. This sectioning permits controlover liquid flow direction, as also discussed further below. Controllingthe direction of liquid flow makes it possible to counteract mechanicalstrains on the lens 102, therefore the flow profile in the X direction(especially during a step) may be different from the flow profile in theY direction (especially during a scan).

FIG. 3 illustrates the same structure as in FIG. 1, except that thedirection of the liquid flow is reversed. As will be appreciated by oneof ordinary skill in the art, the ability to reverse the direction ofliquid flow is important in a practical photolithographic system, sincethe direction of wafer motion is normally not limited to just onedirection. Similarly, it will be appreciated by one of ordinary skill inthe art that, as in FIG. 2, the wafer 101 can move both in the Xdirection and the Y direction. Thus, dividing the housing 103 intoquadrants permits the direction of liquid flow to be adjusted for anydirection of wafer movement.

FIG. 4 illustrates an embodiment of the present invention in additionaldetail. As shown in FIG. 4, the lens 102 is mounted in the housing 103.The housing 103 has the annular channels 105A, 105B, through whichliquid flows in and out from a liquid supply system (not shown in thesefigures). From the channel 105A, the liquid then enters a first largeplenum 215A. It then flows through a diffuser screen 412A, into a firstsmall plenum 414A (which is typically smaller than the first plenum215A). The diffuser screen 412A helps remove the turbulence and airbubbles that may be present in the first large plenum 215A. The diffuserscreen 412 also acts as a pressure drop screen.

The first small plenum 414A also acts as a pressure chamber. From thefirst small plenum 414A, the liquid then flows through a plurality ofmicrochannel nozzles (micronozzles) 416A, arranged in a form of amicroshower. Thus, by the time the liquid reaches the micronozzles 416,the pressure at the entry to all the micronozzles 416 is uniform, andturbulence and gas bubbles have been substantially removed from theliquid. After the micronozzles 416, the liquid flows into the clearaperture area 216 under the lens 102, such that the space between thelens 102 and the wafer 101 is filled with the liquid.

In the clear aperture area 216, the liquid flow is uniform with height,and free of turbulence, bubbles, striations and other imperfections thataffect optical image quality.

On the other side of the clear aperture area 216, the liquid once againflows through a set of microchannel nozzles 416B, into a second smallplenum 414B, through a diffuser screen 412B, into a second large plenum215B and out through the channel 105B.

Thus, with the relative motion of the wafer 101 from left to right inFIG. 4, the wafer 101 creates a “dragging effect” on the liquid. Thedirection of the liquid flow therefore needs to be from right to left,to counteract the “dragging effect,” and result in substantially uniformvelocity profile.

In FIG. 4, 420 designates effective fluid velocity profile within theclear aperture area 216 as induced by wafer 101 motion. 421 designatescounter-injected fluid velocity profile from the microchannel nozzles416, yielding near net-zero resultant fluid velocity at the interfacebetween the lens 102 and the liquid in clear aperture area 216.

The microchannel nozzles 416 also refresh (i.e., replace) the workingliquid from time to time (which may be necessary to prevent itsdisassociation over time, since exposure to intense electromagneticradiation may break down the molecules of the liquid), so as to precludethermal gradients from causing refractive distortions and image qualitydegradation. Avoiding dissociation of liquid (for example water) due toconstant flow is another advantage. At the short exposure wavelength,water can dissociate at approximately 2.86 J/cm² RT and normal P turnsto 4.75*10⁻¹⁹ J per molecule. At 193 nm with one photon carries1.03*10⁻¹⁸ J. Additionally, keeping the liquid refreshed allows tomaintain a constant temperature of the liquid. The liquid may berefreshed during exposure, or between exposures.

The micronozzles 416 also act as a buffer against inertial shearingforces between the optics and the liquid. Note that the shearing forceis dv defined by the equation

${F = {A \cdot \mu \cdot \frac{\mathbb{d}v}{\mathbb{d}x}}},$where A is the area, μ is a viscosity parameter, x is a distancevariable, and v is the velocity. The shearing force is approximately 1Newton in the case of a typical 100 micron gap between the wafer 101 andthe lens 102. Neutralizing these shearing forces is accomplished byinertially dampening the relative accelerative motion between the lens102 and fluid. This is accomplished by simply creating fluidic motion ina direction opposite to scanning. The microchannel nozzles 416 also actas a buffer against inertial shearing forces between the optics andfluid.

Additionally, the housing 103 includes a system for supplying gas toremove any excess liquid from the wafer 101. The housing 103 includes asupply side annulus 406A for gas inflow from a gas supply system (notshown in FIG. 4), a gas seal 410A, which bridges the distance to thewafer 101 and makes a “squeegee” so as to contain and remove any excessliquid, and a return side gas outflow annulus 405A (through which excessliquid is removed). The excess liquid may be removed through the returnside gas outflow annulus 405A, together with the exhausted gas. Asimilar structure may be found in an opposite quadrant of the housing103, as shown on the left side of FIG. 4. The gas supply system works inconjunction with the liquid supply system, whenever there is liquid flowpresent, and, consequently, need only be turned on when there is liquidflow in the clear aperture area 216.

As noted above, in FIG. 4, with the wafer movement from left to right,the liquid flow is “in” at channel 105A, and “out” at channel 105B. Whenthe scan direction is reversed, the liquid flow reverses as well.

FIG. 5 shows a partial isometric view of the micronozzle structure areaof FIG. 4. The channels 105A-105D (not shown in FIG. 5) are connected toouter tubes 507A-507D, through which liquid is supplied. Similarly,though not shown in this figure, the annuli 405, 406 may be connected totubular gas couplings.

FIG. 6 illustrates an example of a liquid exhaust velocity profile thatmay be used in the present invention. As will be appreciated by one ofordinary skill in the art, a “natural” velocity profile is not uniformwith height in FIG. 4, but rather may have a vertical gradient, whichcan cause optical distortion. To compensate for this natural gradient,different lengths of tubes (micronozzles 416) may be used, as shown inFIG. 6. In FIG. 6, the micronozzle length ranges from a maximum of L₁ toa minimum of L₂, resulting in approximately the velocity profile at theexit of the micronozzles 416 shown on the left of FIG. 6. The longer themicronozzle 416, the lower the output velocity of the liquid from thatparticular micronozzle. Furthermore, the micronozzles 416 themselves mayhave different diameters, if needed to further control the velocityprofile. Note further that the tubes of the micronozzles 416 need notnecessarily be parallel to the wafer 101, to further control thevelocity profile.

The height of the liquid above the wafer 101, in a typical system, isapproximately 100 microns. Greater height generally results in a needfor more micronozzles in 416A due to a larger volume in which velocityprofile needs to be controlled.

Thus, with careful selection of the lengths, diameters and orientationsof the micronozzles 416, the velocity profile in the clear aperture area216 of the wafer 101 may be controlled, resulting in a substantiallyuniform velocity profile throughout the clear aperture area 216, therebyimproving exposure quality. In essence, the velocity profile generatedby a structure such as shown in FIG. 6 may be “opposite” of the“natural” profile that would exist otherwise. Thus, the characteristicsof the micronozzles 416 are tailored to result in a substantiallyuniform velocity profile.

During scanning, the wafer 101 moves in one direction, while the liquidis recirculated and injected in the opposite direction. The effect ofthe present invention is therefore to neutralize the liquid velocityprofile induced by the scanning motion, causing inertial dampeningbetween the lens 102 and the liquid. In other words, the net effect is a“zero” net inertia and velocity profile steering away from motion.Depending on the direction of the liquid flow, either a reduction orelimination of shear forces, or a reduction in optical distortions mayresult. Thus, the immersion lithographic process is capable ofperforming at peak levels due to constant fluid refresh, avoidance ofgas bubbles, and the buffering of opto-fluidic vibrations.

Note further that while the liquid in the plenum 215 may have turbulenceand gas bubbles, by the time it travels through the diffuser screen 412,the flow is uniform. Therefore, after passing through the diffuserscreen 412, the plenum 414, and exiting from the micronozzles 416, theliquid flow has a desired velocity profile, substantially withoutimperfections caused by striations, opto-fluidic vibrations, turbulence,gas bubbles, and other non-uniformities, resulting in improved imagequality.

As noted above, the bottom surface 108 of the lens 102 need not be flat.It is possible to use a lens 102 with a curved bottom surface 108, andcompensate for any induced velocity profile non-uniformities with anappropriate arrangement of micronozzle lengths, diameters, andorientations, to result in a near-uniform velocity profile.

The micronozzles 416 may be constructed using conventional lithographictechniques on silicon material. On a microscopic scale, the micronozzles416 resemble a honeycomb material composed of tubes that are stacked ina staggered formation that exhibits key characteristic dimensions ofhydraulic diameter and length. The micronozzles 416 may be flared outinto the clear aperture area 216.

Typical tubular diameters of the micronozzles 416 may vary, for example,from a few microns to tens of microns (e.g., 5-50 microns), and in somecases, up to 5 mm in diameter, and lengths of between about 10 to 100diameters. Other lengths and/or diameters may be used. Slits, ratherthan round nozzles, may also be used. The number of micronozzles perunit area may also be varied.

For 193 nanometer imaging, the liquid is preferably water (e.g.,deionized water), although other liquids, for example, cycle-octane,Krypton® (Fomblin oil) and perfluoropolyether oil, may be used.

The present invention results in a number of benefits to a liquidimmersion photolithographic system. For example, in a step and scansystem, transmission is improved, and there is less distortion. Dustparticles in the air cannot enter the clear aperture area 216 betweenthe lens 102 and the wafer 101, since the liquid itself does not containany dust, and the presence of the liquid acts as a barrier to the dustbeing present in the clear aperture area 216 during exposure.Preferably, the liquid is brought in after the wafer 101 has been loadedonto a wafer stage, and removed before the wafer 101 is unloaded. Thisminimizes dust and particulate contamination. Additionally, other waysof keeping the liquid from spilling during wafer exchange are possibleas well, and the present invention is not limited to just the approachdescribed above.

The fluid velocity profile induced by the scanning motion isneutralized, causing inertial dampening between lens 102 and theshearing fluid. Aside from acting as inertial dampers, the micronozzles416 serve to refresh the working fluid volume, thereby eliminatingrefractive distortions due to thermal gradients created by the lightsource. A side benefit of the micronozzles 416 is their ability todiscourage the formation of gas-bubbles during volume refresh. Also, thesize of these micronozzles 416 prevents the formation of gas-bubblesthat plague more conventional refresh techniques. All of these benefitsallow the use of generally existing photolithographic tools andwavelengths to define much smaller features on a semiconductor surface.

In an embodiment, there is provided a liquid immersion photolithographysystem comprising: an exposure system that exposes a substrate withelectromagnetic radiation and includes a projection optical system thatfocuses the electromagnetic radiation on the substrate; a liquid supplysystem that provides liquid flow between the projection optical systemand the substrate; and a plurality of micronozzles arranged around aperiphery of the projection optical system so as to provide asubstantially uniform velocity distribution of the liquid flow betweenthe substrate and the projection optical system.

In an embodiment, the plurality of micronozzles include a plurality oftubes of varying lengths. In an embodiment, the varying lengths of thetubes provide a velocity profile that compensates for non-uniformities.In an embodiment, the liquid supply system includes: an input channelfor delivering the liquid into a first plenum; a first diffuser screenthrough which the liquid can flow into a second plenum, wherein theliquid can then flow into the micronozzles. In an embodiment, the liquidsupply system further comprises: a second plurality of micronozzlesremoving the liquid from the exposure area into a third plenum; a seconddiffuser screen through which the liquid flows into a fourth plenum; andan output channel through which the liquid is circulated. In anembodiment, the projection optical system includes a housing with a gasseal between the housing and the substrate. In an embodiment, thehousing includes a plurality of annular channels connected to the gasseal through which negative pressure is maintained around the exposurearea so as to remove stray liquid. In an embodiment, the micronozzlesare between 5 microns and 5 millimeters in diameter. In an embodiment,the micronozzles are slit-shaped. In an embodiment, at least some of themicronozzles include a portion that flares out into an area between thesubstrate and the projection optical system. In an embodiment, adirection of the liquid flow is reversible. In an embodiment, the liquidsupply system includes at least three channels through which liquid canflow. In an embodiment, the liquid supply system compensates fornon-uniformities in a velocity profile.

In an embodiment, there is provided a liquid immersion photolithographysystem comprising: an exposure system that exposes an exposure area on asubstrate with electromagnetic radiation and includes a projectionoptical system; means for providing a liquid flow between the projectionoptical system and the exposure area; and a first microshower at oneside of the projection optical system that provides the liquid flowhaving a desired velocity profile when the liquid flow is present in theexposure area.

In an embodiment, the microshower includes a plurality of tubes ofvarying lengths. In an embodiment, the varying lengths of the tubesprovide a velocity profile that compensates for non-uniformities. In anembodiment, the system further comprises a liquid supply system thatincludes: an input channel for delivering the liquid into a firstplenum; a first diffuser screen through which the liquid can flow into asecond plenum, wherein the liquid flows into the exposure area throughthe microshower. In an embodiment, the liquid supply system furthercomprises: a second microshower for removing the liquid from theexposure area into a third plenum; a second diffuser screen throughwhich the liquid can flow into a fourth plenum; and an output channelthrough which the liquid can circulate out of the exposure area. In anembodiment, the projection optical system includes a housing with a gasseal between the housing and the substrate. In an embodiment, thehousing includes a plurality of channels through which negative pressureis maintained around the exposure area so as to remove stray liquid. Inan embodiment, the microshower has micronozzles that are between 5microns and 5 millimeters in diameter. In an embodiment, at least someof the micronozzles include a portion that flares out into the exposurearea. In an embodiment, the micronozzles are slit-shaped. In anembodiment, a direction of the liquid flow is reversible. In anembodiment, the liquid supply system includes at least three channelsthrough which liquid can flow. In an embodiment, the microshowercompensates for non-uniformities in the velocity profile due toscanning.

In an embodiment, there is provided a liquid immersion photolithographysystem comprising: an exposure system that exposes an exposure area on asubstrate with electromagnetic radiation and includes a projectionoptical system; and a liquid flow between the projection optical systemand the exposure area having a velocity profile that compensates forrelative motion of the exposure system and the substrate.

In an embodiment, there is provided a liquid immersion photolithographysystem comprising: an exposure system that exposes an exposure area on asubstrate with electromagnetic radiation and includes a projectionoptical system; and a plurality of micronozzles around a periphery of alens of the projection optical system that provide a liquid flow in theexposure area.

In an embodiment, there is provided a liquid immersion photolithographysystem comprising: an exposure system that exposes a substrate withelectromagnetic radiation and includes a projection optical system thatfocuses the electromagnetic radiation on the substrate; and a liquidsupply system that provides liquid flow between the projection opticalsystem and the substrate, wherein a direction of the liquid flow may bechanged so as to compensate for direction of movement of the substrate.

In an embodiment, the system further includes a plurality ofmicronozzles arranged around a periphery of the projection opticalsystem so as to provide a substantially uniform velocity distribution ofthe liquid flow between the substrate and the projection optical system.In an embodiment, the plurality of micronozzles include a plurality oftubes of varying lengths. In an embodiment, the varying lengths of thetubes provide a velocity profile that compensates for non-uniformities.In an embodiment, the liquid supply system includes: an input channelfor delivering the liquid into a first plenum; a first diffuser screenthrough which the liquid can flow into a second plenum, wherein theliquid can then flow into the micronozzles. In an embodiment, the liquidsupply system further comprises: a second plurality of micronozzlesremoving the liquid from the exposure area into a third plenum; a seconddiffuser screen through which the liquid flows into a fourth plenum; andan output channel through which the liquid is circulated. In anembodiment, the liquid supply system compensates for non-uniformities ina velocity profile.

In an embodiment, there is provided a method of exposing a substratecomprising: projecting electromagnetic radiation onto the substrateusing a projection optical system; delivering a liquid flow between theprojection optical system and the substrate; and controlling a velocityprofile of the liquid flow to as to provide a substantially uniformvelocity profile.

In an embodiment, the method further comprises removing excess liquidfrom the substrate using a gas supply system. In an embodiment, themethod further comprises reversing direction of the liquid flow.

In an embodiment, there is provided a method of exposing a substratecomprising: projecting electromagnetic radiation onto the substrateusing a projection optical system; delivering a liquid flow between theprojection optical system and the substrate; and changing a direction ofthe liquid flow so as to compensate for a change in a direction ofmovement of the substrate.

In an embodiment, the method further comprises removing excess liquidfrom the substrate using a gas supply system.

Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.

The present invention has been described above with the aid offunctional building blocks and method steps illustrating the performanceof specified functions and relationships thereof. The boundaries ofthese functional building blocks and method steps have been arbitrarilydefined herein for the convenience of the description. Alternateboundaries can be defined so long as the specified functions andrelationships thereof are appropriately performed. Also, the order ofmethod steps may be rearranged. Any such alternate boundaries are thuswithin the scope and spirit of the claimed invention. One skilled in theart will recognize that these functional building blocks can beimplemented by discrete components, application specific integratedcircuits, processors executing appropriate software and the like or anycombination thereof. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. An apparatus comprising: a projection opticalsystem configured to expose a substrate with a radiation beam, theprojection system having an optical element; a movable table configuredto move relative to the optical element; and a liquid supply systemconfigured to supply liquid to a space between the projection system andthe table, wherein, in use, the liquid contacts a surface of the opticalelement, the liquid supply system comprising: a plurality of inlets tosupply the liquid to the space, the inlets located above the table andlower than the surface of the optical element, and an extractor toremove liquid from the space, the extractor comprising a two-dimensionalarray of extraction openings and including an extraction opening locatedabove the table and lower than at least one of the inlets.
 2. Theapparatus of claim 1, wherein the inlets are arranged to surround a pathof the radiation beam from the projection optical system.
 3. Theapparatus of claim 1, wherein each of the inlets open so that, in use,the liquid flow from the inlets is substantially parallel to a surfaceof the substrate exposed by the projection optical system.
 4. Theapparatus of claim 1, wherein the extraction opening located above thetable and lower than at least one of the inlets is at least oneextraction opening of the two-dimensional array of extraction openings.5. The apparatus of claim 1, wherein the extraction openings are in astaggered formation.
 6. The apparatus of claim 1, wherein the pluralityof inlets are configured to provide a liquid flow along the scanningdirection to an exposure area.
 7. The apparatus of claim 1, comprising afirst plurality of the inlets on a first side of a path, through thespace, of the radiation beam and a second plurality of the inlets on asecond side of the path opposite the first side.
 8. The apparatus ofclaim 7, comprising a third plurality of the inlets on a third side of apath, different from the first and second sides, and a fourth pluralityof the inlets on a fourth side of the path opposite the third side. 9.The apparatus of claim 1, wherein the liquid supply system comprises ahousing having an open aperture through which the radiation beam isarranged to pass and the inlets are arranged to supply the liquid toabove the aperture, wherein, in use, the liquid from the inlets flowsthrough the aperture to under a bottom surface of the housing.
 10. Adevice manufacturing method, comprising: projecting a patternedradiation beam through a liquid onto a target portion of aradiation-sensitive substrate; moving the substrate; supplying theliquid using a plurality of inlets, wherein the inlets are located abovethe substrate and lower than a surface of an optical element used toproject the patterned radiation beam, wherein the surface contacts withthe liquid; and removing liquid using an extractor comprising atwo-dimensional array of extraction openings including removing liquidvia an extraction opening located above the substrate and lower than atleast one of the inlets.
 11. The method of claim 10, wherein the inletssurround a path of the patterned radiation beam.
 12. The method of claim10, wherein the inlets open so that, in use, the liquid flow from theinlets is substantially parallel to a surface of the substrate ontowhich the patterned radiation beam is projected.
 13. The method of claim10, wherein the extraction opening located above the substrate and lowerthan at least one of the inlets is at least one extraction opening ofthe two-dimensional array of extraction openings.
 14. The method ofclaim 10, wherein the extraction openings are in a staggered formation.15. The method of claim 10, wherein the plurality of inlets provide aliquid flow along the scanning direction to an exposure area.
 16. Anexposure apparatus comprising: a projection optical system configured toexpose a substrate to a radiation beam, the projection system having anoptical element; a movable table configured to move relative to theoptical element; and a liquid supply system configured to supply liquidto a space between the projection system and the table, wherein, in use,the liquid contacts the optical element, the liquid supply systemcomprising a plurality of inlets to supply the liquid; and a twodimensional array of extraction openings to extract liquid from thespace, wherein: each of the inlets is located above the table and lowerthan a surface of the optical element, and a first group of theplurality of the inlets located on a first side of a path, through thespace, of the radiation beam and a second group of the plurality of theinlets located on a second side of the path opposite the first side, athird group of the plurality of the inlets located on a third side ofthe path, different from the first and second sides, and a fourth groupof the plurality of the inlets located on a fourth side of the pathopposite the third side, and at least part of the two dimensional arrayof extraction openings is located above the table and lower than atleast one of the plurality of inlets.
 17. The apparatus of claim 16,wherein the liquid supply system comprises a housing having an openaperture through which the radiation beam is arranged to pass and theinlets are arranged to supply the liquid to above the aperture, wherein,in use, the liquid from the inlets flows through the aperture to under abottom surface of the housing.
 18. An apparatus comprising: a projectionoptical system configured to expose a substrate with a radiation beam,the projection system having an optical element; a movable tableconfigured to move relative to the optical element; and a liquid supplysystem configured to supply liquid to a space between the projectionsystem and the table, wherein, in use, the liquid contacts a bottom-mostsurface of the optical element, the liquid supply system comprising: ahousing, above the table and with respect to which the table is movable,configured to at least partly confine liquid in the space, the housingcomprising a plurality of inlets in a surface of the housing, whereinthe inlets supply the liquid to the space, the inlets located above thetable and lower than the surface of the optical element and each of theinlets open so that, in use, the liquid flow from the inlets issubstantially parallel to a surface of the substrate exposed by theprojection optical system, and an extractor to remove liquid from thespace, the extractor including a two-dimensional array of extractionopenings in a surface of the housing.
 19. The apparatus of claim 18,wherein at least one of the openings of the array of extraction openingsis located lower than the inlets and above the table.
 20. The apparatusof claim 18, wherein the housing comprises an open aperture throughwhich the radiation beam is arranged to pass and the inlets are arrangedto supply the liquid to above the aperture, wherein, in use, the liquidfrom the inlets flows through the aperture to under a bottom surface ofthe housing.